1. Field of the Invention
The present invention relates to a digital signal processing apparatus, a digital signal processing method, a digital signal recording apparatus, a digital signal reproducing apparatus, and a digital video-audio signal recording and reproducing apparatus that handle a plurality of types of audio data with different bit widths.
2. Description of the Related Art
In recent years, an apparatus that records digital audio data and digital video data to a record medium and that reproduces them therefrom is becoming common. Such an apparatus is for example a digital video tape (cassette) recorder.
In addition, since a surround system as an audio reproducing system that spatially forms a sound field and improves presence of a reproduced sound is becoming common, it is desired to increase the number of channels for audio apparatuses. Moreover, to handle multiple languages, it is necessary to increase the number of channels. FIG. 1 shows an example of the structure of a digital audio apparatus 300 that processes audio data of eight channels. The apparatus 300 has four input terminals each of which can input serial audio data of two channels.
Serial audio data according to for example AES/EBU (Audio Engineering Society/European Broadcasting Unit) standard is input to each terminal. FIGS. 2A, 2B, and 2C show the format of audio data according to the AES/EBU standard. Two channels of serial audio data are alternately sent every half period of a frame sequence FS based on a sampling frequency (see FIG. 2A). In FIG. 2A, the forward side and the backward side of the time series are the LSB side and the MSB side, respectively. Data is followed by bits V, U, C, and P that are control and parity bits.
Up to 24 bits of audio data can be sent per sample. 16 bits of audio data per sample are placed on the backward side every half period of the frame sequence FS (see FIG. 2B). As shown in FIG. 2C, 16 bits of audio data are composed of eight bits of the middle portion of 24 bits and eight bits of the upper portion thereof.
The serial audio data is sent to an audio recording encoder 301. The audio recording encoder 301 converts the serial audio data into parallel audio data. The parallel audio data of each channel is stored in packets having a predetermined length each. After a predetermined process is performed for the packets, an error correction code encoding process is performed for the resultant packets with a product code.
In the encoding process with the product code, data arranged in a matrix is encoded for each symbol (for example, each byte) in the column direction with for example Reed Solomon code. Thus, an outer code parity is generated. Data and the outer code parity are encoded in the line direction. Thus, an inner code parity is generated. Since the outer code parity in the column direction and the inner code parity in the line direction are generated, an error correction code encoding process is performed with the product code.
A data block completed with the inner code parity and the outer code parity is referred to as error correction block. One line of the error correction block corresponds to data of one data packet.
In addition to the error correction code encoding process, to improve the resistance of data against an error, data of each of the eight channels is shuffled in a predetermined data unit. The shuffling process is performed by controlling a memory accessing operation in the error correction code encoding process.
A block ID and a sync pattern are added to each packet that has been encoded with the error correction code and that has been shuffled. Thus, sync blocks are formed. The sync blocks are channel-encoded in a recordable format. The resultant sync blocks are recorded on a record medium 310. In this example, the record medium 310 is a magnetic tape. With record heads disposed on a rotating head portion (not shown), helical tracks are formed and data is recorded thereon.
Audio data recorded on the record medium 310 is reproduced by reproducing heads (not shown) and sent to an audio reproducing decoder 311. The decoder 311 detects a sync pattern of the reproduced signal and extracts sync blocks from the sync pattern. The decoder 311 performs a decoding process with an error correction code corresponding to block IDs stored in the sync blocks and a deshuffling process for correctly arranging the shuffled data. The decoder 311 sets an error flag to data whose error has not been corrected with the error correction code. Such data is corrected by an interpolating process using adjacent data or a muting process.
With a memory used for an error correction code decoding process, data is separated into eight channels of audio data. Audio data of each channel is converted into serial audio data corresponding to the AES/EBU standard. The serial audio data is output from the audio recording encoder 311. The audio data is sent to an amplifier 312 with a D/A converting function for eight channels. The amplifier 312 converts the digital audio data into analog audio signals and amplifies the analog audio signals. The amplified audio signals are sent to speakers 313, 313, . . . The speakers 313, 313, . . . reproduce sounds corresponding to the analog audio signals.
In a multilingual region such as European region, there are many users who desire many channels so as to record audio data in multiple languages to one record medium. On the other hand, production houses that create broadcast materials desire a large bit width per sample rather than a large number of channels so as to accomplish high quality sound.
However, each record medium has the upper limit of record density. Thus, in the conventional record format, the number of channels of audio data and the bit width per sample are fixed to those that satisfy the majority of users. Thus, the conventional system does not meet the needs of users who do not satisfy such fixed specifications.